| 摘要 |
A piston and cylinder assembly, a power assisted steering gear which includes such an assembly and a method of forming a piston for such an assembly. A rack and pinion type power assisted steering gear has a rack member 2 coupled to a piston member 6 slidable within a cylinder 16 and forming therewith a double acting servo motor fluid pressure supply and exhaust from chambers 21 and 22 of which is controlled to provide power assistance to displacement of the rack member 2. The piston member 6 has a piston part 10 integrally formed with rod parts 11 and 12 which extend axially from opposite sides of the piston part. The differential in diameter between the rod parts 11 and 12 and the piston part is provided by radial displacement of a tubular workpiece, preferably by subjecting axial part lengths of the workpiece to a rolling or swaging operation whereby the diameter of the workpiece is progressively reduced to form the rod parts 11 and 12 and so that the latter merge through external transition surfaces 25 of progressively increasing diameter with the piston part 10.
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